Papel de la metaloproteinasa MT4-MMP durante el proceso de angiogénesis en el cerebro en desarrollo

Zusammenfassung

Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels during embryonic development. It is based on the migration of endothelial cells that occurs in a manner dependent on proteases that degrade the extracellular matrix. Matrix metalloproteinases (MMPs) are good candidates in the regulation of sprouting angiogenesis. Within this group is included MT4-MMP, a matrix metalloproteinase anchored to the cell membrane through a glycosylphosphatidylinositol (GPI) domain, which participates in tumor angiogenesis by contributing to the maturation and stabilization of vessels during tumor progression. However, the role of this enzyme in vessel formation during embryogenesis remains unknown. Previous studies from our laboratory have demonstrated the expression pattern of MT4-MMP throughout mouse embryonic development. Specifically, during the formation of the vascular system, MT4-MMP is expressed in the perineural vascular plexus and in the endothelial cells of blood vessels that migrate and enter the embryonic neural tissue After confirming the expression of MT4-MMP in the neural tube and the embryonic hindbrain, our results suggest that this enzyme is necessary for the correct angiogenesis of the vascular plexus in the subventricular region of the hindbrain. Analysis of the vascular phenotype using the embryonic hindbrain of Mt4-mmp deficient mice (Mt4-mmp-/- ) revealed defects in angiogenesis when compared with wild-type (Mt4-mmp+/+) embryos. Furthermore, in vitro assays to assess endothelial cell migration directed by chemotactic stimuli demonstrated that the presence of MT4-MMP is required for endothelial cell migration induced by VEGF and to a lesser extent by CXCL12. Moreover, to elucidate whether these defects observed in the mutant hindbrain are a direct consequence of the absence of MT4-MMP in endothelial cells, we analyzed the vascular phenotype in mice that have deleted this metalloproteinase specifically in endothelial cells (Mt4-mmpiΔEC). This line was generated by crossing mice expressing tamoxifen-inducible Cre recombinase under the control of the vascular endothelial cadherin 5 promoter (Ve-Cdh5)- CreERT2 with mice having Mt4-mmp exon 2 flanked by loxP sites (Mt4- mmploxP/loxP). The results show that the specific deletion of MT4-MMP in the endothelium has important consequences on embryonic hindbrain angiogenesis as it results in an aberrant angiogenesis in the subventricular zone. In this context, the lack of MT4-MMP compromises both the number and morphology of embryonic macrophages that play an important role in angiogenesis. Taken together, the results of this work demonstrate that MT4-MMP develops an important role during embryonic angiogenesis and the specific deletion of this metalloproteinase in endothelial cells severely impairs vascularization of the subventricular plexus of the embryonic hindbrain. Moreover, this action of MT4-MMP is not only affecting the endothelial cell, but seems to affect embryonic microglia as well.